allow symbol_intern_string_literal lint in test modules

Signed-off-by: onur-ozkan <work@onurozkan.dev>

compiler/rustc_lint/src/tests.rs

@@ -1,3 +1,5 @@
+#![cfg_attr(not(bootstrap), allow(rustc::symbol_intern_string_literal))]
+
 use rustc_span::{Symbol, create_default_session_globals_then};
 
 use crate::levels::parse_lint_and_tool_name;